Glass is typically made of silicates that are melted to form a clear, transparent, solid material. The fundamental molecular structural unit of conventional glass is a SiO44− tetrahedron. Ordinary float glass (named for its production process whereby a molten ribbon of glass is floated on molten metal to provide a smooth surface) includes additional amounts of soda (Na2O), usually in the form of sodium carbonate or nitrate during the production process, lime (CaO) and other oxides (usually aluminum and magnesium oxides) to form a soda-lime-silica structure known colloquially as soda-lime glass. Other specialized glass can be prepared by the introduction of other additives and constituents.
It is sometimes highly desirable for conventional glass to have hydrophobic (water repellant) surface properties when employed in certain end-use applications, such as for automotive window glass. Various proposals exist to impart hydrophobic (water-repellant) properties to glass substrates. For example, U.S. Pat. Nos. 4,263,350, 4,274,856, 5,665,424 and 5,723,172 (the entire content of each being incorporated expressly hereinto by reference) disclose generally that glass surfaces can be coated with a vapor deposited layer of an chloroalkylsilane, such as dimethyldichlorosilane (DMDCS) so as to improve their hydrophobicity and/or release properties. Other proposals exist whereby a fluoroalkylsilane (FAS) coating may be employed to “cap” an underlayer on a glass substrate so as to improve coating durability. Please see in this regard, U.S. Pat. Nos. 5,328,768, 5,372,851, 5,380,585 and 5,580,605 (the entire content of each being incorporated expressly hereinto by reference). In addition, International Application WO 00/25938 (the entire content of which is expressly incorporated hereinto by reference) discloses that a silicon film consisting of chains of siloxane groups each terminating in an end molecule which reacts with water to form an OH group, may be capped by further reaction of that OH group with trimethylchlorosilane to form trimethylchlorosiloxane.
In commonly owned, U.S. patent application Ser. No. 09/921,303, filed on Feb. 1, 2001 (the entire content of which is expressly incorporated hereinto by reference) there are disclosed coated substrates (preferably glass) and methods which exhibit improved hydrophobicity and durability. In some of the especially preferred embodiments disclosed therein, coated substrates and methods are provided which include a SiOx-containing anchor layer comprised of a controllably humidified vapor phase deposition of a chlorosilyl group containing compound (typically silicone tetrachloride), and a hydrophobic capping layer chemically bonded to the SiOx-containing anchor layer.
It has now been discovered that certain performance enhancements, such as enhanced chemical and weather resistance, may ensue by the vapor deposition of methyltrichlorosilane over a SiOx-containing anchor layer on transparent substrates (e.g., glass) so as to form a film of polymethylsilsesquioxane thereon.
Specifically, in accordance with the present invention, substrates are provided which have a hydrophobic surface coating comprised of the reaction products of methyltrichlorsilane (MTCS) and dimethyldichlorosilane (DMDCS). Most preferably the substrate is glass. An anchor layer is most preferably formed directly onto the glass substrate surface by means of the application of a humidified reaction product of silicon tetrachloride, followed by the vapor-deposition of MTCS as a cross-linking layer. The hydrophobic layer of MTCS and DMDCS may then be applied over the cross-linking layer of MTCS. A capping layer formed of trimethylchlorosilane (TMCS) may then be vapor deposited onto the hydrophobic layer.
These and other aspects and advantages will become more apparent after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.